Instrumented heat exchanger and method for estimating a lifespan of said heat exchanger

ABSTRACT

A heat exchanger including:a plurality of adjacent rectangular frames, each rectangular frame defining an inner volume wherein a fluid is apt to flow,a partition wall arranged between each adjacent frame and separating the inner volumes from each other,a closing wall arranged on each rectangular end frame and intended for closing the inner volume of said rectangular end frames,a plurality of fluidic inlets, each in fluidic communication with an inner volume and a plurality of fluidic outlets, each in fluidic communication with an inner volume, said fluidic inlets and outlet being situated on the rectangular frames,at least one distributor of fluids arranged for distributing a fluid to at least a part of the fluid inlets,at least one collector of fluids arranged for collecting a fluid coming out of at least a part of the fluidic outlets,at least one temperature gage apt to measure a temperature of the fluid,at least one pressure gage apt to measure a pressure of a fluid,at least one strain gage apt to measure a deformation on the heat exchanger,a communication device apt to receive the measurements from the gages and to send same to a computer processing unit.

TECHNICAL FIELD OF THE INVENTION

The invention relates to the technical field of heat exchangers equippedwith measuring instruments. More particularly, the invention belongs tothe field of industrial heat exchangers.

The invention relates to a heat exchanger equipped with measuringinstruments and to a method for estimating the service life of the heatexchanger by means of measurements made by said measuring instruments.

TECHNOLOGICAL BACKGROUND

Industrial heat exchangers are used in various industries.

As an illustration, in the oil, gas and petrochemical industries,production requires the use of heat exchangers for cooling or heatingfluids. E.g., a gas is cooled for being liquefied and stored in a largevolume for transporting by ship whereas the oil is heated forfacilitating the movement thereof through the supply lines.

In such plants, heat exchangers play a central role in production. Inthe event of a failure of a heat exchanger, the production is affectedor even stopped, generating significant financial losses on a dailybasis.

In some cases, damage to the heat exchanger cannot be repaired.Replacement of the heat exchanger becomes necessary. Such industrialheat exchangers are specific and custom-made, so as to meet the needs ofthe plant. Sometimes large (a plurality of meters) and often complex inthe inner architecture thereof, the manufacture of these heat exchangersrequires a plurality of weeks or months to assemble, bake, cool andfinally verify the leak-tightness. The delivery, often by boat, andfinally the installation on site, extends the period during whichproduction at the plant is interrupted or disrupted.

The initial service life of a heat exchanger is defined by themanufacturer. The service life is established for a normal use of theheat exchanger, i.e. at pressures and temperatures within a predefinedrange. The manufacturer also plans a provisional schedule forinterrupting, for maintenance, the use of the heat exchanger. Theschedule, like the initial service life, is established for a normal useof the heat exchanger.

However, it happens that industrial companies use heat exchangersoutside of the predefined intervals. Such situations occur frequently inthe oil and gas industry. Depending on the prices of each hydrocarbon,it can be interesting to produce a particular hydrocarbon. E.g. the sameheat exchanger is used for producing a hydrocarbon in the morning andanother hydrocarbon of a different type in the afternoon.

Such interruptions followed by resumptions of production to which areadded different operating temperatures and pressures for eachhydrocarbon lead to a premature wear of the heat exchangers. Suchpremature wear distorts the planned schedule of shutdowns for themaintenance of the heat exchanger and reduces the service life thereof.

The invention aims to remedy such drawbacks by enabling manufacturers tohave, in real-time, a provisional schedule for maintenance andreplacement of the heat exchanger, which is recalculated according theactual use of the heat exchanger. By following with the plannedmaintenance schedule and the replacement of the heat exchanger asdetermined according to the invention, the untimely shutdown ofproduction due to a failure of the heat exchanger is prevented, andfinancial losses are controlled.

SUMMARY OF THE INVENTION

To this end, a heat exchanger is proposed in the first place, including:

-   -   a plurality of adjacent rectangular frames, each rectangular        frame defining an inner volume wherein a fluid is apt to flow,    -   a partition wall arranged between each adjacent frame and        separating the inner volumes from each other,    -   a closing wall arranged on each rectangular end frame and        intended for closing the inner volume of said rectangular end        frames,    -   a plurality of fluidic inlets, each in fluidic communication        with an inner volume and a plurality of fluidic outlets, each in        fluidic communication with an inner volume, said fluidic inlets        and outlet being situated on the rectangular frames,    -   at least one distributor of fluids arranged for distributing a        fluid to at least a part of the fluidic inlets,    -   at least one collector of fluids arranged for collecting a fluid        coming out of at least a part of the fluidic outlets,    -   at least one temperature gage apt to measure a temperature of        the fluid,    -   at least one pressure gage apt to measure a pressure of the        fluid,    -   at least one strain gage apt to measure a deformation on the        heat exchanger,    -   a communication device apt to receive the measurements from the        gages and to send same to a computer processing unit

Such a heat exchanger makes it possible to have, in real-time, aprovisional schedule of maintenance and replacement of the heatexchanger which is recalculated according to the actual use of the heatexchanger.

Various additional features can be provided alone or in combination:

-   -   the rectangular frames define faces, the heat exchanger defining        a longitudinal axis and a transverse axis extending along a        length and a width, respectively, of said heat exchanger, each        collector and each distributor being attached to the faces and        defining an end junction between both said collector and/or        distributor and the closing walls, at least one junction gage        being arranged on the clos wall, at a first gap distance from        the end junction, comprised between 44 and 150 millimeters, the        first gap distance being measured along the longitudinal axis or        the transverse axis;    -   a plurality of junction gages are arranged on the closing wall,        the junction gages being spaced apart from each other by a first        gap distance comprised between 10 and 500 millimeters;    -   the first gap distance is substantially equal to 50 millimeters;    -   the closing wall defines a rectangle, a central strain gage        being arranged on said closing wall at an intersection of the        diagonals of said rectangle;    -   a plurality of strain gages are arranged on the closing wall,        aligned along the longitudinal axis of said heat exchanger;    -   the strain gages arranged on the closing wall are spaced apart        by a second gap distance measured along the longitudinal axis,        the second gap distance being comprised between 0.6 meters and        1.6 meters;    -   the second gap distance is substantially equal to 1 meter;    -   the heat exchanger includes at least one sealing bar for        separating the inner volume of a frame into at least two        sub-volumes, each sub-volume being suitable for receiving a        different fluid, said sealing bar extending along the transverse        axis or the longitudinal axis, and wherein the heat exchanger        comprises at least one strain gage arranged on the closing wall,        said strain gage being situated at a second gap distance from        the sealing bar comprised between 10 and 50 millimeters, the        second gap distance being measured along the longitudinal axis        when the sealing bar extends along the transverse axis and along        the transverse axis when the sealing bar extends along the        longitudinal axis;    -   a plurality of strain gages are arranged around the sealing bar        on the closing wall, the strain gages being spaced apart from        each other by a third gap distance measured along the        longitudinal axis when the sealing rod extends along the        transverse axis, and along the transverse axis when the sealing        bar extends along the longitudinal axis, said third gap distance        being between 10 and 500 millimeters;    -   the at least one sealing bar defines sub-rectangles on the        closing wall, each sub-rectangle corresponding, in a projection        on the said closing wall, to a sub-volume, and wherein a central        strain gage is arranged on said closing wall at an intersection        of the diagonals of each sub-rectangle;    -   a plurality of strain gages are arranged on each sub-rectangle        of the closing wall, aligned along the longitudinal axis of said        heat exchanger, and wherein said strain gages are spaced apart        from each other by a fourth gap distance measured along the        longitudinal axis, the fourth gap distance being comprised        between 0.6 meters and 1.6 meters and preferably substantially        equal to 1 meter.

Secondly, an assembly comprising a heat exchanger as describedhereinabove and a computer processing unit, is proposed.

Thirdly, a method is proposed for estimating a service life of a heatexchanger by means of an assembly as described hereinabove, the heatexchanger having a predetermined initial service life wherein the methodcomprises:

-   -   a step of continuous measurement of the temperature of the fluid        by means of the temperature gage,    -   a step of continuous calculation of a mechanical stress by means        of measurement of the temperature of the fluid,        -   a step of storage of the calculated mechanical stresses in            memory,    -   a step of continuous measurement of the pressure of the fluid by        means of the pressure gage,    -   a step of calculation of a mechanical stress by means of the        measurement of the pressure of the fluid,        -   a step of storing the calculated mechanical stresses in            memory,    -   a step of continuous measurement of a mechanical stress by means        of the strain gage,        -   a step of storage of the measured mechanical stresses in            memory,    -   a step of determination of a series of ranges of mechanical        stress values,    -   a step consisting in counting occurrences wherein the stored        mechanical stress falls within a range of values established        during the step of determination of a series of ranges of        values,    -   a step of calculation of an estimate of a service life by        comparing the occurrences of the step with a database.

BRIEF DESCRIPTION OF FIGURES

Other features and advantages of the invention will appear duringreading the following description, the understanding of which will besupported by to the enclosed drawings, wherein:

FIG. 1 is a perspective view of a heat exchanger according to a firstembodiment of the invention,

FIG. 2 is another perspective view of the heat exchanger shown in FIG. 1,

FIG. 3 is a top view of the heat exchanger shown in FIG. 1 ,

FIG. 4 is a perspective view of heat exchanger according to a secondembodiment of the invention,

FIG. 5 is a schematic representation of a method according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a heat exchanger 1 according to the invention. Alongitudinal axis X extending along a length L of the heat exchanger 1is defined in the first place, corresponding to the largest dimensionthereof. Secondly, a first transverse axis Y substantially perpendicularto the longitudinal axis X and extending along a width I of the heatexchanger 1, is defined. Finally, a second transverse axis Zsubstantially perpendicular to the axes X and Y and extending along aheight H of the heat exchanger 1, is defined.

The heat exchanger 1 comprises a plurality of frames 2. As can be seen,the frames 2 have a rectangular shape. Each frame 2 is made byassembling a plurality of substantially rectilinear bars 3 beveled ateach of the ends thereof, so as to form a substantially right angle. Theframes 2 are adjacent to each other. In other words, the frames 2 areoverlaid one on top of the other. Each rectangular frame 2 defines aninner volume 4.

The heat exchanger 1 includes partition walls 5. A partition wall 5 isarranged between each rectangular frame 2. Thereby, a given rectangularframe 2 is not in immediate contact with an adjacent rectangular frame2. A partition wall 5 separates the rectangular frames 2 from eachother. The partition walls 5 separate the inner volume 4 of therectangular frames 2 from one another, thereby creating compartmentsalong the axis Z.

On either side of the heat exchanger 1, the latter includes an end frame6, identical to the other rectangular frames 2 but located at the lowerand upper ends 7, 8. A closing wall 9 is arranged on each end frame 6,for closing the inner volume 4 thereof.

As can be seen in FIG. 2 , each frame 2, with the exception of the endframes 6, includes at least one fluidic inlet 10. Each fluidic inlet 10of a given frame 2 is in fluidic communication with the inner volume 4of the given frame 2.

In the same way, each frame 2 except the end frames 6 has at least onefluidic outlet 31. Each fluidic outlet 31 of a given frame 2 is influidic communication with the inner volume 4 of the given frame 2.

As can be seen in the drawings, the fluidic inlets 10 are substantiallyaligned along the axis Z and the fluidic outlets 31 are alsosubstantially aligned along the axis Z.

The heat exchanger 1 includes at least one distributor 11 of fluids andat least one collector 12 of fluids. The distributor 11 and thecollector 12 of fluids have a substantially identical shape. Same is acurved sheet metal part defining a closed volume. The distributor 11 andthe collector 12 are provided with a supply line 13 and with a dischargeline 14, respectively, opening onto the closed volume. The supply pipe13 is used for conveying the fluid into the closed volume of thedistributor 11 and the discharge pipe 14 is used for discharging thefluid from the closed volume of the collector 12.

Hereinafter, distributors and collectors are referred to, indistinctly,by the expression “heads”.

The rectangular frames 2 define faces 16, 17, namely two lateral faces16 extending along the axis X and two transverse faces 17 extendingalong the axis Y. The heads can be attached to the lateral faces 16and/or to the transverse faces 17, defining a junction between saidheads 11, 12 and said faces 16, 17. The heads 11, 12 extend over theentire height H, measured along the axis Z, of the heat exchanger 1.Thus, the heads 11, 12 are attached both to the rectangular frames 2 viaa first junction 18 which extends substantially along the axis Z and tothe closing walls 9 via a second junction 19 which extends substantiallyalong the axis X or Y along the face 16, 17 on which said heads 11, 12are positioned. Hereinafter, the first junctions 18 and the secondjunctions 19 are called lateral junctions 18 and end junctions 19,respectively.

The distributor 11 of fluid thus arranged is used for distributing thefluid towards the fluidic inlets 10. The collector 12 of fluids thusarranged is used for collecting the fluid leaving the fluidic outlets31.

According to a preferred embodiment, the junction is welded so as torigidly attach the heads 11, 12 to the rectangular frames and to theclosing walls.

Advantageously, the heat exchanger 1 comprises at least one temperaturegage 20 apt to measure a temperature of the fluid.

Advantageously, the heat exchanger 1 comprises at least one pressuregage 21 apt to measure a pressure of the fluid.

Advantageously, the heat exchanger 1 includes a plurality of straingages 22 apt to measure deformations on the heat exchanger 1.

The heat exchanger 1 further includes a communication device 23 apt toreceive the measurements from the different gages 20, 21, 22 and to sendsaid measurements to a computer processing unit 24.

Advantageously, the invention also relates to an assembly 25 comprisinga heat exchanger 1 and a computer processing unit 24.

As can be seen in the drawings, the strain gages 22 are advantageouslyarranged on the closing walls 9. The heat exchanger 1 includes so-called“junction” strain gages 22, hereinafter called junction gages 26. Thejunction gages 26 are situated in the vicinity of the end junctions 19and arranged on the closing walls 9. The junction gages 26 are situatedat a first gap distance D1 from the end junctions 19, comprised between44 and 150 millimeters. The first gap distance D1 is measured along thelongitudinal axis X.

Such arrangement of the junction gages 26 is advantageously used forobtaining measurements of the deformation stresses in a zone of the heatexchanger 1 prone to mechanical rupture and hence to leak.

Advantageously, the heat exchanger 1 can comprise a plurality ofjunction gages 26 arranged on the closing walls 9. The junction gages 26are spaced apart from each other by a first gap distance D2 comprisedbetween 10 and 500 millimeters. The first gap distance D2 is measuredalong the axis X when the head 11, 12 is situated on one of the lateralfaces 16 and along the axis Y when the head 11, 12 is situated on one ofthe transverse faces 17.

In a preferred embodiment, the first gap distance D2 is substantiallyequal to 50 millimeters.

Such a first gap distance D2 makes it possible to obtain a precisedistribution of the stress in the vicinity of the end junction 19.

The end junctions 19 extend over a length substantially equal to a widthof the heads 11, 12. As can be seen in the drawings, the junction gages26 are arranged substantially parallel to the end junctions 19 in a zonecorresponding to the length of the end junction 19.

Advantageously, junction gages 26 can be arranged beyond the length ofthe end junctions 19. An additional junction gage 26 can be arrangedbeyond the length of the end junction 19.

Hereinafter, reference is made to FIGS. 1 and 2 illustrating a firstembodiment.

As can be seen in particular in FIG. 2 , the closing walls define arectangle.

Advantageously, a so-called central strain gage is arranged on theclosing walls 9 at the intersection of two diagonals d of the rectangleformed by each of said closing walls 9.

The central strain gage 27 is used for measuring the stresses in a zoneof the closing walls 9 where the deformations are particularlysignificant.

Advantageously, a plurality of strain gages 22 are arranged on theclosing walls 9. The strain gages 22 are aligned along the axis X.

The aligned arrangement of a plurality of strain gages 22 including thecentral strain gage 27 makes it possible to measure the stresses alongthe heat exchanger 1 along the axis X. The applicant determined that thedeformations along the exchanger 1 along the longitudinal directionthereof and passing through the center of the closing walls 9 areparticularly likely to reduce the service life thereof.

Advantageously, the strain gages 22 aligned with the closing walls 9 arespaced apart from each other by a second gap distance D3 measured alongthe axis X. The second gap distance D3 is between 0.6 meters and 1.6meters. Preferentially, the second gap distance D3 is substantiallyequal to 1 meter.

The strain gages 22 thus arranged make it possible to mesh the closingwalls 9 in order to obtain reliable measurements.

Hereinafter, reference is made to FIG. 3 illustrating a variant ofembodiment.

The heat exchanger 1 includes sealing bars 28. The sealing bars 28separate the inner volume 4 of a frame 2, into two sub-volumes. In otherwords, the sub-volumes form sealed compartments. The sealing bars 28thus allow a first fluid to flow through a first compartment 29 and asecond fluid to enter a second compartment 30, without the fluidsmixing.

In the drawing shown in FIG. 3 , the sealing bars 28 are arranged alongthe axis Y. However, same can also be arranged along the axis X. In FIG.3 , the sealing bar 28 is visible in order to facilitate understanding.From the outside of the heat exchanger, the sealing bars 28 are notvisible because same are located in the rectangular frames.

When the heat exchanger 1 comprises sealing bars 28, as is the case inthe second embodiment, a plurality of strain gages 22 are arranged onthe closing walls 9, around the sealing bars 28.

Advantageously, the strain gages 22 are situated at a second gapdistance D4 from the sealing bar 28, which is comprised between 10 and50 millimeters. When the sealing bar 28 is arranged along the axis Y, asis the case in the second embodiment, the second gap distance D4 ismeasured along the axis X. When the sealing bar 28 is arranged along theaxis X (not shown), the second gap distance D4 is measured along theaxis Y.

The strain gages 22 thus arranged make it possible to measure thestresses around the sealing bar 28. Indeed, the zone surrounding thesealing bar 28 can be the seat of leaks.

The strain gages 22 located around the sealing bar 28 are spaced apartfrom each other by a third gap distance D5 comprised between 10 and 500millimeters. The third gap distance D5 is measured along the axis Y whenthe sealing bars 28 are arranged along the axis Y as is the case in FIG.4 . The third gap distance D5 is measured along the axis X when thesealing bars 28 are arranged along X (not shown).

The strain gages 22 thus arranged make it possible to mesh the zonearound the sealing bars 28 in order to detect as well as possibleexcesses which are potentially dangerous for the heat exchanger 1 anduseful in the calculation of the service life of said heat exchanger 1.Indeed, analyses carried out by the applicant were used fordemonstrating the fact that the zones around the sealing bars 28 causedeformations on the closing wall 9.

As can be seen in FIG. 3 , the sealing bar 28 defines sub-rectangles onthe closing wall 9. Each sub-rectangle corresponds to a compartment 29,30 projected along the axis Z onto the closing walls 9. Eachsub-rectangle includes a central strain gage 27 arranged at anintersection of the diagonals d of said sub-rectangles, on the closingwalls 9.

Each sub-rectangle corresponds to an inner sub-volume within a frame.

It has been determined by the applicant that deformations in the centralzone of each sub-rectangle have an impact on the service life of theheat exchanger 1. The central strain gage 27 arranged at said placeadvantageously makes it possible to measure the deformations in saidzone.

As can be seen in FIG. 3 , a plurality of strain gages 22 are arrangedon each sub-rectangle of the closing wall 9. The strain gages 22 arealigned along the X axis.

The aligned arrangement of a plurality of strain gages 22 including thecentral strain gage 27 makes it possible to measure the stresses alongeach sub-rectangle on the closing walls 9. The applicant determined thatthe deformations of the sub-rectangles on the closing wall 9 along thelongitudinal direction of the latter and passing through the center ofthe sub-rectangles are particularly likely to reduce the service lifethereof.

The strain gages 22 are spaced apart from each other by a fourth gapdistance D6 comprised between 0.6 meters and 1.6 meters. The fourth gapdistance D6 is substantially equal to 1 meter.

The strain gages 22 thus arranged make it possible to mesh the closingwalls 9 in order to obtain reliable measurements.

Hereinafter, a method 35 for estimating a service life of the heatexchanger 1 will be described. The estimation method 35 applies to theheat exchanger 1 described hereinabove whichever embodiment described.The heat exchanger 1 has a known initial service life. The initialservice life is calculated by the manufacturer of the heat exchanger 1.

The estimation method comprises a first step E1 of measurement of thetemperature of the fluid, by means of the temperature gages 20.

During a second step E2, the computer processing unit 24 calculates, inreal-time, a thermo-mechanical stress for each temperature measurementperformed. The thermo-mechanical stress is calculated using thefollowing formula:

σ_(th(T)) =E·α·ΔT

-   -   where    -   E is the coefficient of elasticity of the material of the        closing walls,    -   α is the coefficient of thermal expansion of the material of the        closing walls,    -   ΔT is the temperature measured between two different fluids        separated by a partition wall 5.

In a third step E3, the calculated thermo-mechanical stresses are storedin a computer memory.

The method 35 further comprises a fourth step E4 of continuousmeasurement of the pressure, by means of the pressure gages 21.

During a fifth step E5, the computer processing unit 24 calculates, inreal-time, a mechanical pressure stress for each pressure measurementperformed.

In a sixth step, the calculated mechanical pressure stresses are storedin a computer memory.

The method comprises a seventh step E7 of continuous measurement of themechanical stresses on the closing walls 9, by means of the strain gages22.

In an eighth step E8, the measured mechanical stresses are stored.

The method further comprises a ninth step E9 of determining a series ofranges of mechanical stress values. Such ranges of values are determinedby taking the interval between the maximum value and the minimum valueof the previously calculated and measured stresses. The interval betweenthe minimum and maximum is discretized so as to obtain ranges of values.The discretization can be variably coarse depending on the precisionsought. As an example, a discretization can be performed with a stepequal to 10. According to such example, but not limited to, the intervalbetween extrema is divided into 10 ranges of values.

The method includes a tenth step E10 during which the stress calculatedand stored in memory are associated with a range of values. In otherwords, whenever a stored stress has a value within a range of values,the stored stress being associated with the corresponding range ofvalues.

The method 35 comprises an eleventh step E11 during which the number ofoccurrences for each range of values is determined. In other words, fora given range of values, it is determined how many times the previouslycalculated and measured stresses fall within the given range of values.

In this way, it is possible, in a twelfth step E12 of the method, todetermine an estimation of a service life. The above is done in acomparative way with a database empirically developed by performing manylaboratory tests.

1-14. (canceled)
 15. A heat exchanger including: a plurality of adjacentrectangular frames, each rectangular frame defining an inner volumewherein a fluid is apt to flow, a partition wall arranged between eachadjacent frame and separating the inner volumes from each other, aclosing wall arranged on each rectangular end frame and intended forclosing the inner volume of said rectangular end frames, a plurality offluidic inlets, each in fluidic communication with an inner volume and aplurality of fluidic outlets, each in fluidic communication with aninner volume, said fluidic inlets and outlet being situated on therectangular frames, at least one distributor of fluid arranged fordistributing a fluid to at least a part of the fluid inlets, at leastone collector of fluid arranged for collecting a fluid coming out of atleast a part of the fluidic outlets, at least one temperature gage aptto measure a temperature of the fluid, at least one pressure gage apt tomeasure a pressure of the fluid, at least one strain gage apt to measurea deformation on the heat exchanger, a communication device apt toreceive the measurements from the gages and to send same to a computerprocessing unit.
 16. The heat exchanger according to claim 15, whereinthe rectangular frames define faces, the heat exchanger defining alongitudinal axis (X) and a transverse axis (Y) extending along a length(L) and a width (I), respectively, of said heat exchanger, eachcollector and each distributor being attached to the faces and definingan end junction between both said collector and/or distributor and theclosing walls, at least one junction gage being arranged on the closingwall at a first gap distance (D1) from the end junction, comprisedbetween 44 and 150 millimeters, the first gap distance (D1) beingmeasured along the longitudinal axis (X) or the transverse axis (Y). 17.The heat exchanger according to claim 16, wherein a plurality ofjunction gages are arranged on the closing wall, the junction gagesbeing spaced apart from each other by a first gap distance (D2)comprised between 10 and 500 millimeters.
 18. The heat exchangeraccording to claim 17, wherein the first gap distance (D2) issubstantially equal to 50 millimeters.
 19. The heat exchanger accordingto claim 15, wherein the closing wall defines a rectangle, a centralstrain gage being arranged on said closing wall at an intersection ofthe diagonals (d) of said rectangle.
 20. The heat exchanger according toclaim 19, wherein a plurality of strain gages are arranged on theclosing wall, aligned along the longitudinal axis (X) of said heatexchanger.
 21. The heat exchanger according to claim 20, wherein thestrain gages arranged on the closing wall are spaced apart by a secondgap distance (D3) measured along the longitudinal axis (X), the secondgap distance (D3) being comprised between meter and 1.6 meter.
 22. Theheat exchanger according to claim 21, wherein the second gap distance(D3) is substantially equal to 1 meter.
 23. The heat exchanger accordingto claim 16, further including at least one sealing bar intended forseparating the inner volume of the frame into at least two sub-volumes,each sub-volume being apt to accommodate a different fluid, said sealingbar extending along the transverse axis (Y) or the longitudinal axis(X), and wherein at least one of the at least one strain gage isarranged on the closing wall, being situated at a second gap distance(D4) from the sealing bar, comprised between 10 and 50 millimeters, thesecond gap distance (D4) being measured along the longitudinal axis (X)when the sealing bar extends along the transverse axis (Y) and along thetransverse axis (Y) when the sealing bar extends along the longitudinalaxis (X).
 24. The heat exchanger according to claim 23, wherein aplurality of the at least one strain gage are arranged around thesealing bar on the closing wall, the plurality of strain gages beingspaced apart by a third gap distance (D5) measured along thelongitudinal axis (X) when the sealing bar extends along the transverseaxis (Y) and along the transverse axis (Y) when the sealing bar extendsalong the longitudinal axis (X), said third gap distance (D5) beingcomprised between 10 and 500 millimeters.
 25. The heat exchangeraccording to claim 23, wherein the at least one sealing bar definessub-rectangles on the closing wall, each sub-rectangle corresponding, ina projection on said closing wall, to a sub-volume, and wherein acentral strain gage is arranged on said closing wall at an intersectionof the diagonals (d) of each sub-rectangle.
 26. The heat exchangeraccording to claim 25, wherein a plurality of the at least one straingage are arranged on each sub-rectangle of the closing wall, alignedalong the longitudinal axis (X) of said heat exchanger, and wherein saidplurality of strain gages are spaced apart from each other by a fourthgap distance (D6) measured along the longitudinal axis, said fourth gapdistance (D6) being comprised between 0.6 meter and 1.6 meter, andpreferentially substantially equal to 1 meter.
 27. An assemblycomprising the heat exchanger according to claim 15 and a computerprocessing unit.
 28. A method for estimating a service life of a heatexchanger by means of the assembly according to claim 27, the heatexchanger having a predetermined initial service life, wherein themethod comprises: continuously measuring the temperature of the fluid bymeans of the temperature gage, continuously calculating a mechanicalstress by means of measurement of the temperature of the fluid, storingthe calculated mechanical stresses in memory, continuously measuring afluid pressure by means of the pressure gage, calculating a mechanicalstress by means of measuring the fluid pressure, storing the calculatedmechanical stresses in memory, continuous measuring a mechanical stressby means of the strain gage, storing in memory the measured mechanicalstresses, determining a series of ranges of mechanical stress values,counting the occurrences wherein the stored mechanical stresses fallwithin a range of values established in the determining of the series ofranges of values, and calculating an estimate of a service life bycomparing the occurrences with a database.
 29. The heat exchangeraccording to claim 18, further including at least one sealing barintended for separating the inner volume of the frame into at least twosub-volumes, each sub-volume being apt to accommodate a different fluid,said sealing bar extending along the transverse axis (Y) or thelongitudinal axis (X), and wherein at least one of the at least onestrain gage is arranged on the closing wall, being situated at a secondgap distance (D4) from the sealing bar, comprised between 10 and 50millimeters, the second gap distance (D4) being measured along thelongitudinal axis (X) when the sealing bar extends along the transverseaxis (Y) and along the transverse axis (Y) when the sealing bar extendsalong the longitudinal axis (X).
 30. The heat exchanger according toclaim 24, wherein the at least one sealing bar defines sub-rectangles onthe closing wall, each sub-rectangle corresponding, in a projection onsaid closing wall, to a sub-volume, and wherein a central strain gage isarranged on said closing wall at an intersection of the diagonals (d) ofeach sub-rectangle.